Dashboard Feb-May 2013

I always like posts that start at the big picture first and the details second. No question that reducing emissions is a total approach problem. From my own situation, a 40 mile Electric range is ideal whereas the 12 mile PiP range is too short. But either still needs to figure out how to make sure the electricity is clean as possible. I still have some interesting decisions to make of how I vote with my wallet.

 

Why is what ?

 

Interesting post Bob, thanks! When you said it had signficantly lower drag I expected a bigger gap. I was already curious how these were defined and estimated so I went and did some reading.. From the process/spec I see it is not exactly rolling, drivetrain and areo, (the EPA calls them rolling, rotating and areo) rather it is litteraly a quadratic fit (although those terms do dominate the respective terms) to a coast down timing process. (I did not get an answer about power-on in neutral but the documents do say testing hybrids with no pure neutral is a problem.)

Given how crude the process is I wondered about the variance between cars. So I went and pulled the data to see what the variance was and if the difference between PiP and Volt was statistically significant. The table you cite has 5 volts being measured and 14 PiPs, with separate data for each car. I computed the average and standard deviations (table below) then ran the simulation again with a 95% confidence interval (i.e. +/- two sigma) on each coefficient.

	Column 1
0	[th] Volt Coef[th]Pip Coef[th] Coefficient Name
1	[tr][td2]26.40285714 ±0.995853307[td2]23.3914 ±1.052487991[td] Target Coef A (lbf)
2	[tr][td2]-0.022314286 ±0.017210697[td2]-0.162728 ±0.007324356[td] Target Coef B (lbf/mph)
3	[tr][td2]0.018682857 ±0.000694879[td2]0.0205906 ±0.00092662[td] Target Coef C (lbf/mph**2)

The graph is below. This analysis suggests the differences are not statistically significant at above 30 or 35mph.

 

Under EPA city cycle, Leaf gets 129 MPGe while Fit EV gets 132 MPGe. I actually average 132 MPGe with PiP on EV miles (city and highway). I am getting 54 MPG on gas also. I am extreme satisfy with the best of both worlds result.

Fit EV is smaller with skinnier tires and weights more than PiP. That can't be good for stopping distance.

Is your situation one or two charges per day?

 

One

 

Ugh. I thought I was somewhat following your most excellent post until this paragraph. Why is the drivetrain not an included factor -- or at least the components that turn when the wheels turn ?

 

Perhaps my misunderstanding has to do with what components are included in the word 'drivetrain' ? I have figured it meant from driveshaft to wheels. Incorrect ?

In a Prius I thought a 'coast-down' spun everything from the PSD to the wheels. Again, incorrect ?

 

Two would change the game dramatically.

You are wise to consider the upstream emission and efficiency as well. It feels good to see big MPG (ev-boosted) and a lot of EV bias people ignores the electricity upstream emission and efficiency (or the lack of).

I think it comes down to this. PiP was designed to maximize efficiency from both fuels (EV experience in city and HV for highway). Volt was designed to maximize EV range and EV experience. Ford Energi's were designed with somewhere in between.

Edit: Forgot to include the interior space. It goes in the order of PiP > Energi > Volt.

 

I read through the specs and the require driving strait to a constats speed, putting it in N and coasting.
My question was about what "N" means to a drivetrain with permanent magnet motors that cannot be clutched out while in N, ... since they will have drag. I think that is what the documents meant about their being issues for the coastdown model in hybrids.. you cannot get rid of the motors.

Why would what test is used matter for the roll down coefficients? Why not include the actual variations across the different cars used, as there were multiple car IDs not just test differences.

 

What is your source of information for those claims? Can you provide a reference (other than your and John's posts here on prisuchat) that supports that as toyota's design goals?

I would say publications support the conclusion the Volt design goals were not what you sate. The Volt's designers set the requirement for EREV (i.e. EV only ability at all speeds), then set the 40mile EV range goal (clearly not maximizing EV range) and then to balance experience cost, MPG and styling.
See these discussions
Detroit Auto Show: It's here. GM's plug-in hybrid is the Chevy Volt Concept
http://www.media.gm.com/content/dam/Media/microsites/product/volt/docs/paper.pdf
GM’s Chevrolet “VOLT” shocks the industry - CleanMPG Forums
Interview with Chevy Volt Chief Designer About the Production Car: Plus Leaked Pictures and Video

Since they designed the Volt from the ground up they did not have as much constraint about packing things in existing space and were free to set a wider range of goals.

I don't know what toyota wanted, and I could find no documents suggesting that was their design goal. THe cloest I found was from Toyota | Toyota Introduces 2012 Prius Plug-in Hybrid
[quote[A key goal for development of the Prius Plug-in was to deliver the optimal balance of performance, range, economy, packaging and affordable price. The new model delivers extended EV range without sacrificing roominess for passengers or for luggage. [/quote]
Which I read as their design was to minimize change while maximize profit while stopping from loosing loyal toyota customers. But I see no evidence in that or any other document that there was an explicit attempt to simultaneously maximize efficacy from both fuels. If efficiency is measured in the vehicle, then more EV is better. If measured some in a larger life-cycle (e.g.wells-to-wheels with or without externalities) then it varies greatly with the source and model and so would not be a well defined measure to "maximize" without specifying which one.

I have not read much about the Ford goals so won't comment on their design goals.

And I think the sales of the various units reflect differences in those design goals in relation to the market. GM has larger total sales, but also spend more on R&D/design/manufacturing. Toytoa may well have maximized their profits, they have retained some 15000 customers that might have gone elsewhere, who paid a premium over the Prius for their plug in, allowing quick recovery of the much lower R&D/design/manufacturing costs.

 

See this post for Q&A with the PiP lead engineer. You posted in that thread so you must be aware. I think this one answered it.

Q: How did you choose the pack size, since you get only 9 to 15 miles of electric range-versus 25 to 40 in, say, a Chevrolet Volt?​

​

A: For the plug-in Prius, it was very important to optimize efficiency for all usages, and to retain the fuel efficiency when operating in hybrid mode. A higher electric range means more weight from a heavier battery, which hurts fuel economy, as well as less space inside. So, we try to make the most efficient vehicle in all operating modes.​

Below is a few snips from SAE paper 2011-37-0033 to support my posts. To me, short trips = city driving. European PiP has EV City button for that purpose.

 

In the article you cite, the engineer clearly start by saying" optimize efficiency for all usages, and to retain the fuel efficiency when operating in hybrid mode." The gets into weight and space.


I.e. he is saying they were not willing to sacrifice hybrid mode efficiency That is not optimizing for the usage of both fuels, its optimizing what they could do in EV without impacting hybrid mode.

The second statement from the engineer was that they try (not do) to make "the most efficient vehicle in all operating modes". But such an optimization does nothing to actually optimize the use of both fuels (which is you content was their design goal) which requires deciding which mode to use when. Nor does such a design produce the optimal balance between modes. To me that Q&A came across as suggesting they did a classic decomposition approach to complex engineering. Separate into parts (HV is an already proven subsystem, so minimize changes and don't loose anything there. Keeping the HV components the same, then do a some constrained optimization on the remaining elements. 62 MPH is not a magic efficiency number, it is set by the limit of the reused parts in their current configuration. Nothing wrong with engineering around cost and reuse of subsystems, just don't confuse that with optimizing for overall fuel efficiency.

The EV city button is because of taxes for nonEV veichles in downtown such as london, have to ensure it will not use the ICE or face fine. (Though if the battery is too low the even using EV city button will not stop it"

The short trips do nothing to support your theory. In fact the article directly contract it and says

Optimizing the use of both fuels (or even optimizing anything to do with efficency) is not listed as a reason at all!




This is a perfectly fine business strategy and their sales don't have to be great to recover the reduced R&D /design/manufacturing costs that approach produces. But lets not confuse it with an attempt to actual optimize the use of both fuels or the overall efficiency of the vehicle.

 

"optimize efficiency for all usages, and to retain the fuel efficiency when operating in hybrid mode."

I read that as, optimize for EV and HV operation modes. When you optimize efficiency for all usages, you optimize the overall efficiency -- resulting in a balance plugin running on either fuel. It was stated that 40kW power and 100km/h speed are more than enough for city driving.

To me, the strategy and the goal are clear -- provide the best of both EV and HV worlds without compromising interior space and controlling the cost.

They knew their ideal owner would only be 40% in the US (for 1st gen production PiP). It is pretty obvious that the later generation with improvement in packaging (new platform) and lithium battery would enable more range, hence higher percentage of ideal owners.

 

Thank you, that was an interesting report.

The e-motor/inverter in the Lexus 600h is a monster.

 

Honestly I am not sure it matters, but I read "all usages" in a more general way, such as short trips in the city, longs trips on the highway, carrying 5 people, getting stuff at Home_Depot ...

Interior volume, vehicle weight, EV and HV efficiency are all required ingredients. There are certain to be trade-offs, and no one spec such as EV efficiency could be assumed to be 'best.' Clearly they were not willing to increase EV range if it made a mess of their other priorities.

Such is world of engineering and customers. GM and the Volt otoh was a study in bailout politics and battery subsidy.

 

From my ownership experience, my EV mile efficiency is about as good as Leaf in the city driving and the gas efficiency of the iconic Prius for HV miles.

Having those advantages in one car (and got it for $25k) makes me smile.